Report on Ruapehu (New Zealand) — December 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 12 (December 1987)
Managing Editor: Lindsay McClelland.
Ruapehu (New Zealand) Declining lake temperature; minor deflation
Please cite this report as:
Global Volcanism Program, 1987. Report on Ruapehu (New Zealand) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:12. Smithsonian Institution.
39.28°S, 175.57°E; summit elev. 2797 m
All times are local (unless otherwise noted)
Crater lake temperature had declined to 17°C by 19 December, 10° lower than when last measured on 12 November. ... Geologists noted that although recent strong inflow of water into the lake had probably contributed to the temperature decrease, a color change suggested decreased heat flow. Minor deflation, following the period of gradual inflation that occurred through 1987, was recorded by the deformation survey. Seismicity has remained generally low since 12 November and there was no sign of recent volcanic activity.
Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake (Te Wai a-moe), is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3,000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.
Information Contacts: P. Otway, NZGS Wairakei.